Making the First Cut

Now that our CNC machine is operational and provisioned, we can begin to test out its capabilities through some basic cuts. Depending on the material and the nature of our project, we can choose to cut or engrave – or do both. For example, we might want to make an engraved plaque but then have the CNC machine shape it out of our work material. We might also want to machine a component that has grooves, countersunk holes, or markings.

This chapter will show you how to do the following:

• Secure your workpiece especially if your ultimate objective is to end up with a finished product cut out of the stock material.
• Select a test pattern to see the various effects. One of the options here is to use a laser to replicate shading effects as might be visible in a photograph. Think of a black and white image and the various shades of gray. You can replicate this using a laser on just about any material.
• Manipulate configuration settings to achieve...

Securing the workpiece

My CNC machines all have tables made of aluminum extrusions, except for one that uses a piece of plate metal. Both would get ruined if I made a mistake and cut through my workpiece and into the table. Eventually the structure would weaken, and I would have to disassemble the entire Y-axis assembly and replace the table – not something I would relish having to do multiple times. Consequently, as has been mentioned before, I like to put a piece of waste board between my workpiece and the table. The waste board is typically made of MDF or plywood and is sacrificial. However, with a thick piece material on top of my table and under the material I am trying to cut or carve, I have to find a way to bolt the material to the waste board and the waste board to the table.

You can purchase waste boards for your 3018 on Amazon or AliExpress easily enough. These often come with countersunk threaded inserts as well, so that you can secure your board to the table...

Selecting test patterns

Whenever I set up a new CNC machine, I attempt to cut a series of basic shapes first and then work my way up to more complex tasks. I prefer to start with some simple carving into MDF or plywood. I try to avoid cutting through the material because I want to test the machine against the material and get familiar with how well it handles certain tasks. Not all machines (or end mills) are created equal, and this is the time where I look for obvious limitations.

Choose your test material and bolt it down to your waste board. I typically start with something that is 20-25 mm (up to 1”) thick or more and set my design to a cut depth of 1 mm or so, gradually increasing the depth of my cuts to see how well they come out. I am effectively carving or engraving here, and for our purposes that’s good enough. You might want to prepare several small test boards so that you can use them to calibrate your machine. By cutting only to an initial depth of 1 mm...

Configuration settings

The settings for any given project or cut will revolve around several parameters. However, in this section, let’s review some basic settings I use to smoke-test every workpiece.

End-mill diameter

You must always determine how much room your toolhead has to move between lines. If you have two cut lines that are very close to each other and the diameter of the end mill will span that gap, a design revision may be needed, or a revised selection of end mill or material will be necessary. Generally speaking, this will be apparent if you look at your toolpath and determine that two cut lines come too close together. Of course, the depth of your cut plays a role here as well. If we have a non-uniform end mill (where the cut width will change with the depth) then the toolpath is something to consider. For most of what I do, I stick with a few common bits for my 3018 machine and so I do not change the bit radius/diameter once I have set it. If I am using...

Different settings for different operations

We have already touched on some of the considerations around settings related to not just what you are cutting, but also how. For a laser, multiple passes where the beam is likely to diffuse inside acrylic may mean wider cut lines and multiple passes (acrylic tends to re-melt if the cut line is thin, requiring higher power beams and multiple passes). When using an end mill most of your settings will be in the G-code generator program. However, there are some basics I have found that serve me well.

If I am engraving wood, I keep the depth to 1-2 mm at most. If I need shading and changes in texture, I will switch to a laser. If I am engraving metal with an end mill I never get deeper than 1 mm and prefer to stay in the realm of 0.2-0.5 mm.

I have broken enough bits trying to find a baseline feed rate for every material I typically work with. This feed rate is calculated based on the bit, the RPM, the material type, and so on. You may...

Summary

The focus of this chapter was on some basic settings for your CNC machine and how to optimize them. We have also learned how to confirm our machine is operating to expectations by running some test patterns. As we progress and your experience with your machine grows, you will develop your own test workflow as well as optimum settings for your projects, materials, and end mills. There are many variations here because not all of our 3018 machines are the same (and if you are using something other than a 3018, you definitely have your own tweaking to do).

The next chapter is the opener for a series of special projects. We will have the opportunity to try our hand at setting cut depths and/or depths per pass and look at how we might make the same thing out of different materials. This will allow us to investigate the settings we have discussed here and see what the effects are when we cut soft wood, hardwood, foam, acrylic, and other materials.